Method for the production of a valve seat

ABSTRACT

In a process for producing a valve seat for a cylinder head of an internal combustion engine, by introduction of energy a filler material is fused to the cylinder head at the location at which the valve seat is to be formed. The filler material used is an alloy or mixture of an aluminum-iron alloy and at least one further constituent.

This application claims the priority of German Patent Document No. 10156 196.2, filed 15 Nov. 2001, and PCT/EP02/11682, filed 18 Oct. 2002 thedisclosure of which is expressly incorporated by reference herein,respectively.

BACKGROUND AND SUMMARY OF THE INVENTION

The invention relates to a process for producing a valve seat for acylinder head of an internal combustion engine. Furthermore, theinvention relates to a valve seat arrangement for a cylinder head of aninternal combustion engine.

DE 199 12 889 A1 describes a process of the generic type for producing avalve seat. In this process, a filler material, namely an alloy or amixture of an aluminum-silicon alloy and nickel, is fused to the basematerial of the cylinder head by a laser beam.

DE 35 17 077 C1 describes a process for cladding the valve seat surfaceof a gas exchange valve, in which cladding material preferablyconsisting of a nickel- or cobalt-base superalloy is introduced into anencircling recess at the valve disk.

A process for coating the surface of metallic workpieces with a fillermaterial that is in powder or wire form is described by DE 199 12 894A1.

A further process of this type is described in EP 00 92 683 B1. The basematerial of the cylinder head in this case substantially comprisesaluminum, and either iron or nickel or an alloy containing one of thesetwo metals as its main constituent is used as a filler material forforming the valve seat.

A drawback of such a process is that iron and nickel have asignificantly higher melting point than the cylinder head, whichconsists of aluminum. This can mean that the cylinder head has alreadymelted under the application of a laser beam when the filler material isjust starting to melt. Moreover, the iron which was previously in liquidmay solidify while the aluminum is still in the form of a melt. Thisleads to the formation of intermetallic phases in the boundary regionbetween the iron material and the aluminum material, which can give riseto a very brittle microstructure. Therefore, it is difficult to achievea homogeneous join between the valve seat which is to be created and thebase material of the cylinder head; the different surface tensions ofthe materials also play a major role in this respect.

EP 02 28 282 B1 describes a cylinder head consisting of an aluminumalloy. The valve seats of this cylinder head are formed from a plated-oncopper alloy layer.

However, if copper is used as a material for valve seats, in particularin the case of diesel engines, the sulfur which is contained in thediesel fuel can attack the copper, resulting in problems with regard toexhaust emissions and corrosion. Therefore, the use of copper for valveseats is only suitable for spark-ignition internal combustion enginesand therefore cannot be employed in an economically viable way.

DE 196 39 480 A1 describes a process for the internal coating ofcylinder liners by means of filler materials in powder form which arealloyed on by laser radiation.

A process for the surface treatment of light metal components, inparticular of light metal pistons of internal combustion engines, with astrength-enhancing and/or wear-resistant filler material is described byDE 22 00 003 A1.

It is an object of the present invention to provide alternativeprocesses for producing valve seats for the cylinder head of an internalcombustion engine.

According to an embodiment of the invention, this object is achieved byuse of a filler material that is an alloy or mixture of an aluminum-ironalloy and at least one further constituent.

Given a suitable design of the cylinder head, an alloy of this type canbe an alloy of the same type as the base material of the cylinder head,which often consists of an aluminum-silicon alloy. This allows for goodmetallurgical bonding without the formation of brittle intermetallicphases at the interface between the coating or filler material and thebase material. Consequently, there is little tendency for cracks toform. The iron content in the alloy used for the filler material inaccordance with the invention advantageously increases the hardnessthereof.

In an alternative embodiment a filler material is used comprising analloy or mixture of aluminum and titanium.

In such an embodiment, the advantages which have already been referredto above in connection with the use of an alloy of the same type as thebase material, such as reduced likelihood of cracks forming, also apply.An intermetallic phase of titanium and aluminum is advantageouslyformed, bringing benefits with regard to the hardness, the resistance towear and the thermal stability of this alloy.

In still another embodiment, a filler material is used comprising analloy or mixture of an iron-carbon alloy and at least one furtherconstituent.

This composition is in principle based on conventional materials ofvalve seat rings fitted as separate parts, but can likewise be appliedby means of the melting process according to the invention and has ahigh hardness and very good wear properties.

In yet another embodiment filler material is used comprising an alloy ormixture of a nickel-chromium alloy and at least one further constituent.

An alloy of this type allows high resistances to temperature and wear tobe achieved and, given a suitable selection of the further constituent,has very good tribological properties.

A common feature of all of the above embodiments is that the bonding ofthe valve seat to the cylinder head is durable and can therefore be usedsuccessfully in practice. Furthermore, the mixtures and alloys describedcontribute to a considerable increase in the process reliability.

In another embodiment, the invention comprises a cylinder head of aninternal combustion engine.

According to an embodiment, the valve seat arrangement comprises annularregions which widen the valve seats and partially overlap one another.As a result the regions between the actual valve seats, known as thevalve lands, also consist of the higher-quality material used for thevalve seats. This has the advantage of considerably reducing thesusceptibility of these valve lands and of the associated region of therespective combustion chamber of the cylinder head to cracking. As aresult, higher thermal and mechanical loading of the cylinder head ispossible in this region.

BRIEF DESCRIPTION OF THE DRAWINGS

Advantageous configurations and refinements of the invention will emergefrom the subclaims and from the exemplary embodiments which are outlinedbelow with reference to the drawing, in which:

FIG. 1 shows a valve, arranged in a cylinder head of an internalcombustion engine, with a valve seat;

FIG. 2 shows an enlarged view of an alternative embodiment of the valveseat;

FIG. 3 shows an enlarged view of a further alternative embodiment of thevalve seat;

FIG. 4 shows an enlarged view of a further alternative embodiment of thevalve seat;

FIG. 5 shows an enlarged view of a further alternative embodiment of thevalve seat;

FIG. 6 shows an enlarged view of a further alternative embodiment of thevalve seat;

FIG. 7 shows the process according to the invention as a single-stageprocess; and

FIG. 8 shows the process according to the invention as a two-stageprocess.

FIG. 1 shows part of a cylinder head 1 of an internal combustion engine,the remainder of which is not shown. The cylinder head 1 has, in amanner which is conventional, an intake port 2, which in the presentcase could also be formed as an exhaust port. The intake port 2 isclosed and opened by a gas exchange valve 3, which is referred to belowsimply as valve 3 for the sake of simplicity, so that a fuel/air mix canenter a combustion chamber 4 of the cylinder head 1 from the intake port2.

The cylinder head 1 is provided with a valve seat 5, against which thevalve 3 bears in its closed state, thereby disconnecting the intake port2 from the combustion chamber 4.

FIGS. 2 to 6 illustrate various embodiments of the valve seat 5, whilethe process used to produce the corresponding valve seat 5 will bedescribed further on in the description, with reference to FIGS. 7 and8.

The valve seat 5 shown in FIG. 2 is accommodated in an encircling groove6 of the cylinder head 1. The valve seat has a thickness of approx.d=1-6 mm, is provided with a radius r at the corner point which islocated completely inside the cylinder head 1, and the angle α formed bythe connecting surface of the valve seat 5 and the cylinder head 1 withrespect to the longitudinal axis of the valve 3 is approx. α=0°-45°. Thestructure described, in particular the thickness d which is indicated,results in a sufficient wearing reserve for any remachining, for examplein the event of a repair being required.

FIG. 3 illustrates a further embodiment of the valve seat 5, which issimilar to that shown in FIG. 2. However, the angle α with respect tothe longitudinal axis of the valve 3 is negative. In other words thevalve seat 5 has an undercut with an angle of approx. α=2-15° withrespect to the groove 6 in the cylinder head 1, causing the coating orvalve seat 5 to be wedged such that it cannot drop out of the groove 6.

The thickness d of the valve seat 5 shown in FIG. 4 is approx. d=0.5-5mm. The angle α of the connecting surface between the valve seat 5 andthe cylinder head 1, which in this case is designed to be straight, withrespect to the longitudinal axis of the valve 3 is approx. α=45°,although slight deviations are of course also possible.

In all the embodiments shown in FIGS. 2, 3 and 4, geometric spacesavings are possible compared to conventional seat ring geometries.

A further embodiment of the valve seat 5 is shown in FIGS. 5 and 6; inthese cases, the valve seat 5 takes up a much larger area than in thecase of the embodiments described above. In other words, the valve seats5 are widened by an annular region 5 a. The individual regions 5 apartially overlap one another, so that the regions between the actualvalve seats 5, namely what are known as the valve lands, also consist ofthe higher-quality material for the valve seats 5. This considerablyreduces the susceptibility of the valve lands and the associated regionof the respective combustion chamber 4 of the cylinder head 1 tocracking, so that in this region a higher thermal and mechanical loadingof the cylinder head 1 is possible. The thickness d of the valve seat 5is d=1-10 mm.

FIG. 7 and FIG. 8 show two different processes for producing the valveseat 5. A filler material 7 in the form of a powder is applied to thebase material of the cylinder head 1. The filler material can be a lightmetal alloy, such as for example an aluminum-silicon alloy. Theconstituents of the filler material 7 will be dealt with in more detailbelow. As an alternative to an aluminum-silicon alloy as the basematerial of the cylinder head 1, other light metal alloys can be used,and if appropriate also gray cast iron or other alloys.

To apply the filler material 7, a nozzle 8, which discharges the fillermaterial 7 toward the cylinder head 1, is arranged in the region of thevalve seat 5 which is to be formed. When the filler material 7 hits thecylinder head 1, in the embodiment shown in FIG. 7 it is simultaneouslymelted, together with the outer layer of the base material of thecylinder head 1, by a laser beam 9 in order to produce a melt 10 at thecylinder head 1. As an alternative to using the laser beam 9 as energysource, it is also possible to use an electron beam (not shown) in orderto produce the melt 10 from the filler material 7 by introduction ofenergy.

To achieve a continuous process, the nozzle 8 and the laser beam 9 areconstantly advanced in a circular motion. When the laser or electronbeam 9 has been removed from the melt 10 in the direction of advanceindicated by the arrow A, the melt solidifies to form a layer 11 whichforms the valve seat 5.

FIG. 8 shows an alternative process for producing the valve seat 5, inwhich the filler material 7 is applied to the cylinder head 1 orintroduced into the groove 6, in the form of a paste, a wire, a sinteredbody or powder preform. The filler material is then melted to form themelt 10 by means of the laser beam 9 or alternatively by means of anelectron beam. The layer 11 which forms the valve seat 5 is formed fromthe melt 10 after the laser beam 9 has been removed in the directionindicated by arrow A. This process is referred to as a two-stageprocess.

If the filler material 7 has already been heated or partially orcompletely melted by the uptake of energy even before it strikes thesurface of the cylinder head 1, it is possible to reduce the amount ofenergy introduced by the primary energy source, i.e. the laser beam 9 orthe electron beam. As a result, the base material of the cylinder head 1is only slightly melted, with the result that the occurrence of brittlephases and the formation of cracks in the interface between the cylinderhead 1 and the valve seat 5 are reduced. This allows materials which areotherwise relatively unsuitable to be used as filler material 7. Thisprocedure is particularly suitable for the two-stage process describedabove.

In a manner which is not illustrated, a magnetic field, which impartscontours to and/or intimately mixes the filler material 7 and/or themelt 10 formed from the filler material 7, may be provided in the regionof the valve seat 5, leading to a more homogeneous distribution of thesubstances within the melt 10. Furthermore, it is in this way possiblefor any pores which may be present in the melt 10 to be eliminatedthrough the expulsion of gases.

Various types of mixtures and alloys can be used for the filler material7 both in the process shown in FIG. 7 and in the process shown in FIG.8, and these mixtures and alloys are listed below:

The filler material 7 used may firstly be an alloy or mixture of analuminum-iron alloy and at least one further constituent. Thealuminum-iron alloy may contain 6-13% by weight of iron and 87-94% byweight of aluminum.

As further alloying constituent, the filler material 7 may contain 1-3%by weight of vanadium and/or 1-3% by weight of silicon.

Furthermore, it is conceivable for the filler material 7 to contain30-55% by weight of nickel and then if appropriate 3-15% by weight ofcopper.

Alternatively, the filler material 7 may also contain 5-20% by weight ofnickel and then if appropriate 35-45% by weight of copper.

The use of nickel and copper gives rise to nickel-aluminum and/orcopper/aluminum phases, which increase the hardness of the valve seat 5.

A further constituent of the filler material 7 may be 0.2-1% by weightof magnesium and 0.2-2% by weight of boron, titanium and/or scandium.This leads to a finer formation of intermetallic phases and an improvedmicrostructural homogeneity.

Moreover, if appropriate it is also conceivable for the filler material7 to contain hard-material components, which consist of a compound of ametal with carbon, oxygen or nitrogen. Hard materials of this typeincrease the wear resistance of the valve seat 5 considerably.

The hard-material components may optionally be distributed homogeneouslythrough the volume of the valve seat 5 or it is possible for thehard-material components to be distributed inhomogeneously through thevolume of the valve seat 5, with the level of the hard-materialcomponents present increasing from the cylinder head 1 toward thesurface of the valve seat 5. The latter alternative, i.e. what is knownas a gradient layer, leads to an increase in the concentration of hardconstituents toward the surface of the valve seat 5, thereby increasingthe hardness properties and therefore the wear properties of the valveseat 5. At the same time, however, this also reduces the susceptibilityto cracking in the joining zone, i.e. at the connecting surface betweenthe valve seat 5 and the cylinder head 1.

The statements which have been made with regard to the advantages of thehard-material components also apply to the nickel and copperconstituents, which on the one hand may be distributed homogeneouslythrough the volume of the valve seat 5 or on the other hand may bedistributed inhomogeneously through the volume of the valve seat 5, withthe level of the nickel and copper constituents present increasing fromthe cylinder head 1 toward the surface of the valve seat 5.

As an alternative to the embodiment with an aluminum-iron alloy or amixture of these metals, it is also possible for the filler material 7used to be an alloy or mixture of aluminum and titanium. In this case,the filler material 7 may, for example, contain 30-40% by weight ofaluminum and 60-70% by weight of titanium. Alternatively, it is alsopossible for the filler material 7 to contain 13-17% by weight ofaluminum and 83-87% by weight of titanium.

In this case, the filler material 7 may contain at least one furtherconstituent, specifically 0.5-5% by weight or 17-50% by weight ofniobium, which is emanately suitable for reducing the tendency towardembrittlement. It is also possible for the filler material 7 to contain0.5-5% by weight of chromium, vanadium, manganese, molybdenum and/ortantalum.

A third option relating to the formation of the filler material 7 mayconsist in using an alloy or mixture of an iron-carbon alloy and atleast one further constituent for the filler material.

In this embodiment of the process, the filler material may contain asfurther constituent 0.5-4% by weight of nickel and/or 0.5-4% by weightof chromium and/or 0.5-4% by weight of manganese and/or 5-15% by weightof molybdenum and/or cobalt. The use of nickel and/or chromium allowsthe formation of carbides, which increase the hardness of the valve seat5. Furthermore, in this context it is possible for the filler material 7to contain 10-25% by weight of copper. Cobalt, copper and molybdenumimprove the lubrication properties, and copper improves the thermalconductivity.

A fourth option for carrying out the process consists in the fillermaterial 7 used being an alloy or mixture of a nickel-chromium alloy andat least one further constituent, in which case the nickel-chromiumalloy may contain 10-30% by weight of chromium and 70-90% by weight ofnickel.

For this embodiment, it is possible for 3-5% by weight of silicon to beused as a further alloying constituent. Further possible alloyingconstituents comprise 3-5% by weight of boron and 3-5% by weight ofiron.

If appropriate, 10-40% by weight of molybdenum may be present in thefiller material 7. Furthermore, it is possible for the filler material 7to contain 5-10% by weight of copper and/or cobalt. Moreover, it ispossible for the filler material 7 to contain 5-12% by weight ofaluminum and 0.1-2% by weight of carbon and/or yttrium.

1-15. (Canceled)
 16. A process for producing a valve seat for a cylinderhead of an internal combustion engine, comprising: fusing a fillermaterial to the cylinder head, by introduction of energy, at a locationwhere a valve seat is to be formed, wherein the filler materialcomprises an alloy or mixture of 30-40% by weight of aluminum and 60-70%by weight of titanium.
 17. The process as claimed in claim 16, whereinthe filler material comprises at least one further constituent.
 18. Theprocess as claimed in claim 17, wherein the further constituentcomprises 0.5-5% by weight of niobium.
 19. The process as claimed inclaim 17, wherein the further constituent comprises 17-50% by weight ofniobium.
 20. The process as claimed in claim 17, wherein the fillermaterial comprises 0.5-5% by weight of chromium, vanadium, manganese,molybdenum or tantalum.
 21. The process as claimed in claim 16, whereinfusing the filler material to the cylinder head comprises introducingenergy using a laser beam.
 22. The process as claimed in claim 6,wherein fusing the filler material to the cylinder head comprisesintroducing energy using an electron beam.
 23. The process as claimed inclaim 16, further comprising providing a magnetic field in the vicinityof the location of the valve seat, said magnetic field impartingcontours to or intimately mixing the filler material or the melt formedfrom the filler material.
 24. The process as claimed in claim 16,further comprising applying the filler material to the cylinder head,wherein applying the filler material to the cylinder head occurs at thesame time as the introduction of energy for fusing the filler material.25. The process as claimed in claim 16, further comprising applying thefiller material to the cylinder head in powder form.
 26. The process asclaimed in claim 16, further comprising applying the filler material tothe cylinder head using a nozzle.
 27. The process as claimed in claim16, further comprising applying the filler material to the cylinder headprior to fusing the filler material to the cylinder head.
 28. Theprocess as claimed in claim 27, wherein applying the filler material tothe cylinder head comprises applying the filler material in powder form.29. A process for producing a valve seat for a cylinder head of aninternal combustion engine, comprising: fusing a filler material to thecylinder head, by introduction of energy, at a location where a valveseat is to be formed, wherein the filler material comprises an alloy ormixture of 13-17% by weight of aluminum and 83-87% by weight oftitanium.
 30. The process as claimed in claim 29, wherein the fillermaterial comprises at least one further constituent.
 31. The process asclaimed in claim 30, wherein the further constituent comprises 0.5-5% byweight of niobium.
 32. The process as claimed in claim 30, wherein thefurther constituent comprises 17-50% by weight of niobium.
 33. Theprocess as claimed in claim 30, wherein the filler material comprises0.5-5% by weight of chromium, vanadium, manganese, molybdenum ortantalum.
 34. The process as claimed in claim 29, wherein fusing thefiller material to the cylinder head comprises introducing energy usinga laser beam.
 35. The process as claimed in claim 29, wherein fusing thefiller material to the cylinder head comprises introducing energy usingan electron beam.
 36. The process as claimed in claim 29, furthercomprising providing a magnetic field in the vicinity of the location ofthe valve seat, said magnetic field imparting contours to or intimatelymixing the filler material or the melt formed from the filler material.37. The process as claimed in claim 29, further comprising applying thefiller material to the cylinder head, wherein applying the fillermaterial to the cylinder head occurs at the same time as theintroduction of energy for fusing the filler material.
 38. The processas claimed in claim 29, further comprising applying the filler materialto the cylinder head in powder form.
 39. The process as claimed in claim29, further comprising applying the filler material to the cylinder headusing a nozzle.
 40. The process as claimed in claim 29, furthercomprising applying the filler material to the cylinder head prior tofusing the filler material to the cylinder head.
 41. The process asclaimed in claim 40, wherein applying the filler material to thecylinder head comprises applying the filler material in powder form. 42.A valve seat arrangement for a cylinder head of an internal combustionengine, having a plurality of valve seats produced using the process asclaimed in claim 1 and comprising said filler material, the valve seatsin each case being widened by an annular region which comprises saidfiller material, wherein the individual annular regions at leastpartially overlap.